Lecture 9-Local Potentials

Question 1

How does the size of a fiber affect resistance?

Answer 1

larger fiber= decreased resistance

Question 2

What does the length constant (lambda) represent?

Answer 2

How FAR a signal will travel before it dissipates (ratio of the membrane resistance/internal restance)

Question 3

How does an increase in membrane resistance affect the number of membrane channels?

Answer 3

increased resistance= less channels

Question 4

How does a decrease in membrane resistance affect the number of membrane channels?

Answer 4

decreased resistance= more membrane channels (membrane is more leaky)

Question 5

How does increasing the membrane resistance affect the time constant?

Answer 5

increased membrane resistance= increased time constant

Question 6

How is the resistance of the membrane affected by opening membrane channels?

Answer 6

more open channels= decreases membrane resistance

Question 7

How does myelin affect the membrane resistance and time constant?

Answer 7

myelin increases the membrane resistance and time and length constant

Question 8

How many length constants does it take for a signal to dissipate?

Answer 8

5 length constants

Question 9

How could you increase the length constant?

Answer 9

increase membrane resistance (less holes) or increase internal resistance (large fiber diameter)

Question 10

Why do we ignore the external resistance when calculating the length constant?

Answer 10

because volume of extracellular fluid is so large the resistance is very close to zero

Question 11

What does a larger capacitance mean?

Answer 11

you need more voltage to “charge up” the membrane

Question 12

What does the time constant represent?

Answer 12

How long it take to charge the membrane (think of the hose example)

Question 13

How does the resistance of the membrane affect the time it takes to charge the membrane (time constant)?

Answer 13

increased resistance= increases time constant (slower signal-good for slow discharge, allows for summation of signals)

decreased resistance= decreases time constant (faster signal-good for quick response)

Question 14

How is a local potential difference from an action potential?

Answer 14

has no threshold and therefore can be graded by amplitude

declines with distance

Question 15

How many time constants are require to reach the full charge value?

Answer 15

5 time constants

Question 16

What controls the time course by which a local potential rises and decays?

Answer 16

resistance and capacitance

Question 17

What does increasing the internal resistance do to the length constant?

Answer 17

an increased internal resistance results in a decreased length constant

Question 18

How are nerve fibers classified?

Answer 18

based on diameter of fiber and degree of myelination

Question 19

What classification of nerve fibers includes the slowest fibers that are either unmyelinated or have very little myelin?

Answer 19

c fibers

Question 20

What classification of nerve fibers contains the largest, heavily myelinated nerve fibers?

Answer 20

A alpha fibers

Question 21

What is Guillan Barre Syndrome?

Answer 21

autoimmune disease that affects the Schwann cells, causing demyelination in the PNS and decreased conduction velocity

Question 22

What does multiple sclerosis cause?

Answer 22

demylelination in the CNS (attack of oligodendrocytes)